The present invention relates to a double-cylinder circular stocking knitting machine with structurally highly simplified cam box.
It is known that double-cylinder stocking knitting machines comprise a lower needle cylinder and an upper needle cylinder, which is arranged upward and coaxially with respect to the lower needle cylinder. In the curved surface of the two needle cylinders there are multiple slots that run parallel to the axis of the cylinders. Inside each one of said slots there is a double- or twin-hook needle, typical of double-cylinder machines. In each slot of the upper needle cylinder there is an upper slider, which can engage the upper hook of the needle arranged in said slot in order to actuate it when it has to knit in the upper needle cylinder, i.e., during the formation of purl stitches.
In each slot of the lower needle cylinder there is a lower slider, which can engage the lower hook of the needle arranged in the same slot in order to actuate it when it has to knit in the lower needle cylinder, i.e., during the formation of plain stitches.
Below the lower slider, inside the same slot, there is a sub-slider, which acts as a memory, and there is a selector, which is used to select the needles that must knit at a given feed or drop and to actuate in a different manner the needles that are moved to knit in order to perform the various knitting processes.
The upper slider and the lower slider are each provided with two heels, which are mutually spaced parallel to the longitudinal extension of the slider, i.e., parallel to the axis of the needle cylinder, and protrude constantly, in a radial direction, from the corresponding slot of the needle cylinders.
The sub-slider also is provided with a heel, which protrudes constantly and radially from the corresponding slot of the needle cylinders.
The selector is generally of the oscillating or elastic type and is provided with main heels, an upper one and a lower one, and with one or more secondary selection heels that are arranged between said two main heels. The upper main heel protrudes constantly, in a radial direction, from the slot of the lower needle cylinder, while the lower main heel can move from an active position, in which it protrudes from the slot, to an inactive position, in which it is fully contained within the slot. The secondary selection heels also protrude from the slot when the selector is in the active position.
The cam box is arranged around the needle cylinders and supports a plurality of cams, which form paths that can be engaged by the heels of the sliders, sub-sliders and selectors so as to cause the intended actuation of the needles when the needle cylinders are actuated rotationally about their axis with respect to the cam box.
In currently commercially available double-cylinder machines, in order to perform the various knitting processes, i.e., in order to vary the paths defined by the cams, many of the cams that actuate the sliders are provided so that they are movable and can be shifted on command toward or away from the needle cylinders, respectively in order to engage or not engage the heels of the sliders.
The presence of the movable cams is a problem, since such cams increase the structural complexity of the cam box and require the use of actuators which, in addition to having to be actuated, must also be controlled in order to avoid accidental interferences between the heels and the cams.
Besides the need to have movable cams, the cam box of known types of double-cylinder machine is extremely complicated and challenging during design, assembly and fine-tuning of the machine.
The aim of the present invention is to solve the above noted problems, by providing a double-cylinder circular stocking knitting machine which, while being able to perform the knitting processes of currently commercially available double-cylinder machines, has a cam box that is structurally simpler.
Within this aim, an object of the invention is to provide a machine in which the use of cams that can move toward and away from the needle cylinders is reduced considerably or even eliminated.
Another object of the invention is to provide a machine that also allows to increase the number and type of processes that can be performed at a same feed or drop of the machine.
This aim and these and other objects that will become better apparent hereinafter are achieved by a double-cylinder circular stocking knitting machine, comprising lower and upper needle cylinders arranged above and coaxially with respect to said lower needle cylinder; multiple slots being formed in the curved surface of said needle cylinders and running parallel to the axis of said needle cylinders; each one of said slots accommodating a twin-hook needle, a lower actuation element arranged in the lower needle cylinder, and an upper actuation element arranged in the upper needle cylinder; each one of said actuation elements being provided with at least one heel suitable to protrude radially from the corresponding slot of the needle cylinder and being actuatable so as to actuate the overlying or underlying needle; a cam box being arranged around the curved surface of said needle cylinders, said cam box having a plurality of cams that form paths that can be engaged by said at least one heel; said needle cylinders being rotationally actuatable about their own axis with respect to said cam box; characterized in that at least said lower actuation element comprises a slider that can detachably engage the lower hook of the overlying needle and, below it, a sub-slider provided with an actuation element that has two heels, an upper one and a lower one, which are mutually spaced along an extension of, and parallel to the axis of the needle cylinders; said actuation element being able to oscillate on a plane that passes through the axis of the needle cylinders in order to assume a first position, in which said lower heel is fully contained within the corresponding slot and the upper heel is extracted from the corresponding slot, or a second position, in which said lower heel is extracted from the corresponding slot and said upper heel is fully contained within the corresponding slot, or a third position, in which said lower heel and said upper heel are both fully contained within the corresponding slot; actuation means being provided which act on said actuation element for its transfer into one of said positions; said plurality of cams of the cam box comprising a first set of cams, which define paths for said lower heel for the actuation of said sub-slider and of the overlying slider in the transfer of the corresponding needle from the lower to the upper needle cylinder and in knitting processes with an alternating motion of the cylinders about their axis, and a second set of cams, which define paths for said upper heel for the actuation of said sub-slider and of the overlying slider in the actuation of the corresponding needle in the formation of drop stitches, in the formation of tuck stitches, and in the transfer of the needle from the upper to the lower needle cylinder.